Add minor improvements

[rszamszur]

Checklist:

• Added tests for changed code where applicable.
• Documentation reflects the changes where applicable.
• Updated the CHANGELOG.md file with your changes.
• My PR is ready to review.

Description of the changes being introduced by the pull request:

• Update .gitignore
• Update .dockerignore
• Update project template .gitignore
• Update project template .dockerignore
• Remove saving to files of flake8 violations in build/metrics.sh script (both for fastapi-mvc and project template).

[codecov-commenter]

Codecov Report

Merging #127 (e01cc46) into master (18fbb9e) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master      #127   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           40        40           
  Lines          800       800           
=========================================
  Hits           800       800           

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[github-actions]

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